Diolefin production



May 15,' 1945. J. P. JONES DIOLEFIN PRODUCTION Filed June 2, 1941 man mzstmz.

INVENTOR- JEAN R JONES BY RWM MM ATTORNEY Patented May 15,1945

, ATonarm monUc'rroN Jean P. Jones, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Application June z, 1941, sensi No. 396,342 s claims. (ci. aso-eso) This invention relates to the production of low boiling diolefln hydrocarbons from more saturated low boiling hydrocarbons heavier than methane. It relates more particularly to the production of dioleiins such as butadiene, pentadiene, isoprene, cyclopentadiene and the like by treating hydrocarbons of 2 to 5 carbon atoms per molecule in a. combination of catalytic dehydrogenation and pyrolysis steps.

An appreciable number of diolefins such as those just mentioned have been known to the art for a number of years. 'I'hese have ibeen produced in a number of-ways which have included cracking of heavier oils,- the inter-reaction oi' acetylene and ethylene to form butadiene, catalytic or thermal conversion of alcohols, both of the same number of carbon atoms per molecule as the .desired diolen and of a fewer number of carbon atoms per molecule, as well `as the dehydrogenation of the corresponding olefins which in turn may have been produced by the dehydrogenation of the corresponding paraillns. Dioleiins have also been reported as being present in the pyrolysis'products of light hydrocarbons,

vincluding even methane. There are enormous quantities of such lighter hydrocarbons which are potentially available for the production of such diolefins, but apparently most ofthe commercial installations and processes to -date have been one of the more involved types previously mentioned rather than the direct conversion of cheap and abundant light hydrocarbons to diolens.

I have now found that I can successfully produce substantial yields of low boiling diolefins in a process in which unsaturated hydrocarbons of 2 and 3 carbon atoms per molecule are converted at elevated temperatures andv low pressures in combination with catalytic delrvdrogenation of normal butane, normal pentane or isopentane. In one modiiication of my process the unsaturated Cz and Cs hydrocarbons are derived from the eiiluent of the catalytic dehydrogenation, and Darts of the eiiiuent of both of these steps are separated in a common separation step to eliminate undesirable constituents and to produce a suitable charge stock for one or both of the conversion steps. The charge to my processmay comprise predominantly or consist of a Single hydrocarbon material such as normal pentane, normal butane, isopentane or cyclopentane, or in one modification it may comprise a mixture of hydrocarbons of up to 5 carbon atoms per molecule which may be derived from a natural gas, but which more preferably will be derived from the effluent o! a cracking still, and thus will contain unsaturated hydrocarbons as well as saturated hydrocarbons, Methane may be present in the charge stock and in the material charged to either of the conversion steps, but will generally not enter extensively into the reactions which take place under the most desirable conditionsl but will be present primarily as a diluent.

It is an object of my invention to-convert low boiling hydrocarbons into low boiling diolefin hydrocarbons.

Another object of my invention is to produce dioleiin hydrocarbons from more saturated hydrol to'5 carbon atoms per molecule areeiilcientlyj converted into dolefin hydrocarbons with high yields. I f Y Further objects and advantages of my inven- 'tion will become apparentfrom the accompanying disclosure and discussion. f v

The features of my invention will now be disclosed and discussed in connection with the accompanying drawing which illustrates diagrammatically by way of a ow sheet a manner of practicing my invention, together with auxiliary steps which maybe incorporated with various modifications, of which the discussion will also catalyst, and the dehydrogenation unit itself is comprised of suitable heating units or furnaces, catalyst chambers and the like known to the art for eiecting and ymaintaining catalytic dehydrogenation of low boiling hydrocarbons. While the dehydrogenation, which is carried out in unit I2, should not `be primarily of any destructive type, I have found that in order to obtain an optimum conversion of the hydrocarbon material hereinafter.

rIAhe eiiluent of the l dehydrogenation passes through pipe I3 and valve I4 to an absorber or fractionating unit I5. The absorber I5 is preferably operated at a substantial superatmospheric pressure, such as one of 600 to 800 or more pounds per square inch, and suitable com-- pression equipment not shown should be inserted between the dehydrogenation unit I2 and the absorber I5, as will be readily appreciated by those skilled in the art. In a preferred modification of my invention, the absorber I5 may not be very large and should be equipped at the top with suitable cooling means I6 to provide a reiiux condensate. The absorber should contain bubble trays or any suitable type of packing known to the art, and in many instances about 8 to 15l bubble trays will be suillcient. The absorber should be operated so that a substantial proportion of the C2 and heavier hydrocarbons including essentially all of the C4 and heavier hydrocarbons are separated as a liquid, and Cz and C3 hydrocarbons together with substantially all of the methane and hydrogen will be separated as a gas. In the modilcation shown, the cooling means I6 cools and condenses the heavier inch gauge and at an elevated temperature such as about 200 F. The material which has been absorbed in absorber 23 is vaporized and passed from the stripper 30 through a pipe 3I and may be passed through a valve 32 and a valve 33 to absorber I5 or a portion thereof may be passed through pipe 34 and valve 35 for subsequent treatment to be described, If desired, a part of this material may be removed from the system through pipe 36 controlled by valve 31. Also` .if desired, any part or all may be passed to separating unit 62, to be described, through pipe 38- and valve 39, from pipe 34, to remove al1 light materials. To aid in the removal of this material from vthe absorption oil a portion of the methane and lighter gases may be passed to a low point of stripper 30 from pipe 24 through pipe 40 controlled by a valve 4I. Lean absorption oil is passed from the bottom of stripper 30 to a pipe 42 controlled by a valve 43 to an accumulator y44 which is provided with a vent 45 controlled by a valve 46. From accumulator 46. the lean absorption oil may be returned to the absorber 23 through pipe41 controlled by a valve 48. A portion of the absorption oil may be removed from the system for purification if desired through pipe 49 controlled by a valve 50. Fresh absorption oil may be added to pipe 41 through pipe 5I controlled by valve 52.

The hea-vier part of the eflluent of the dehydrogenation, and containing substantially all of the C4 and heavier hydrocarbon material together with substantial amounts of C2 and C3 hydrocarbons, is passed as a liquid from the bottom of absorber I5 through `a pipe 60 controlled by a valve 6I to a separating unit 62. Separating unit 62 will comprise various ractionators, stills, solvent extraction units or the like as will be found most suitable for treating a material charged thereto and producing the various fractions desired. In general it will be necessary to separate a hydrocarbon fraction comprising essentially hydrocarbons having the same number of carbon atoms per molecule and the same carbon skeleton structure as that of the hydrocarbon material charged through pipe I0 for recycle to the dehydrogenation unit l2, through pipe 63 hydrocarbons which flow down theabsorber to dissolve and remove all C4 and heavier hydrocarbons, along with some C2 and Ca hydrocarbons.

The gaseous eilluent of absorber I5 passes overhead through pipe I1 and may be removed from the system through pipe 20 controlled by valve 2 I This material, however, is preferably passed through valve 22 in pipe I1 to a low point of absorber 23 wherein it is contacted with a suitable absorption liquid to eiect a separation of C2 and heavier hydrocarbons from methane and lighter material. 'Ihe methane and lighter materialis removed from a high point of absorber 23 through a pipe 24 and may be discharged from the system through valve 25. While the operation of absorber 23 will be discussed in connection'with the use of a light absorption liquid, it will of course be understood that other known means of separationmay be used, suitable modifications of equipment being readily supplied andsubstituted by one skilled in the art. When a light absorption-oil is used, an absorption pressure of 600 to 800 pounds will generally be found expedient.

The rich absorption oil'is passed from the bottom of absorber 23 through pipe 26 and valve 21 and through a heater 26 to the top of a stripper 30. Stripper 30 is operated at a low superatmospheric pressure such as about 25 to 50 pounds per square controlled by a valve 64. `It will also be desirable to separate a fraction comprising the diolefin corresponding to this hydrocarbon material which is recovered in any degree of purity which may be desired for subsequent use, and which is represented by the butadiene fraction which is recovered from separating unit 62 through a pipe 65 controlled by a valve 66. Other dioleiln hydrocarbons which may be present in the dehydrogenation eluentor which may be present in the enluent of the pyrolysis step to be discussed. may be recovered from separating unit 62 through one or more outlets represented by pipe 61 controlled by a valve 66. Undesirable heavy material such as tar may be discharged from the system through pipe 10 controlled by a valve 1I while any light material such as methane or hydrogen may. be-discharged from the system through a pipe 12 controlled by a valve 13.

A Ca-Ca fraction which will contain a substantial proportion of unsaturated hydrocarbons. which willbe primarily ethylene, propylene and perhaps some acetylene, ls removed from separating unit 62 through a pipe 14 controlled by a valve 16 rand is converted at a high temperature oi the order of 1300 to 1700" F. and at a low pressure to produce an optimum yield of low boiling dioletemperature.

.stable metal oxide gel catalysts or natural occurring minerals to promote the desired conversion. The eiliuent of this high temperature conversion is passed through a pipe 'E8 controlled by valve 1S to suitable separation means such as the absorber 8i). The absorber 8@ may be operated under conditions similar to those described for absorber l by the aid of a cooling coil di in the top part which provides suicient cooling for condensation of Ca and heavier hydrocarbons so that gaseous eiliuent from the top thereof is essentially free of .C4 and heavier hydrocarbons. Suitable cooling and compression equipment ,not shown may be inserted in pipe 18 sothat the material undergoing separation in absorber 80 will be at an optimum separation pressure and A gaseous material comprising methane and hydrogen, together with some C2 and Cs hydrocarbons, passes from the top of absorber 80 through a pipe 82 and may be discharged in part or entirely through a valve 83. However, I prefer that a large part or all of this material be passed from pipe 82 through pipe 84 controlled by valve 85 to pipe l1 for treatment in absorber 23 along with a gaseous material eiiluent at the top of absorber I5.

A liquid hydrocarbon material containing substantial amounts of C2 and C: hydrocarbons and substantially. all of the C4 and heavier hydrocarbons present in the effluent from the conversion zone 16 ispassed from a low point of absorber 80 through pipe 90. This material may be discharged from the system through a pipe 9i controlled by a valve 92 for such subsequent separation and other treatment as may be found desirable. However, I prefer to pass a large part or all of this material to separating unit G2 in which provision has already been made for separating hydrocarbonlmixtures of .this kind. All of the material passing from absorber ed through pipe 9i! may be passed directly to separating unit d2 from pipe 9|!! through pipe S3 controlled by a valve 96. In some cases it may be found desirable to separate heavy aromatic hydrocarbons and tar from this stream prior to its introduction into separating unit 62. If such a modification is desirable, the material passing through pipe 90 may be passed through a valve a5 to a simple fractionating unit 98. The undesired heavy hydrocarbon material is 'removed through pipe 97 controlled by valve 98, and low boiling hydrocarbons comprising unreacted C2 and C: hydrocarbons together with the desired diolefins are passed from the top of the fractionating unit 96 through a pipe |00 controlled by a,- valve IM to pipe and separating unit 62.

v My process is sulciently ilexible that it mayl be operated successfully and with high yields on any one of several types of charge stock which l hydrocarbon-.together with a corresponding olen hydrocarbon is available, this material may also be charged to the system through pipe l0. The C: to C4 or Cs fraction which may be separated from the eilluent of any known cracking system for the conversion of heavy oils or from -a unitary conversion of propane and/or butane or the like is also a desirable charge stock for my process. Such a charge is preferably introduced to separating unit 62 through a pipe M12 controlled by a valve N3. In separating unit 62 such a charge stock is separated into a Ca-Ce fraction suitable for charging to the conversion unit 'I6 and into one or more C4 or Cs fractions, each comprising essentially a hydrocarbon material of a single number of carbon atoms per molecule and of a single carbon atom skeleton structure, which may be charged to a catalytic dehydrogenation unit I2 through pipe S3. If the material charged through pipe 02 contains hydrocarbons such that 2 separate catalytic dehydrogenation units are desirable for treating the hydrocarbons separated therefrom, such units may be made a part of my process although not shown in detail, as will be readily appreciated by one skilled in the art. In such a modiiication, the eilluent of each such dehydrogenation unit may pass to a common absorber i5 or each may be treated in a separate absorbing unit with the liquid material eilluent therefrom passing separately to separating unit 62.

As previously stated, a dehydrogenation carried out in unit I2 is preferably carried out in the presence of a suitable dehydrogenation catalyst. It has been foundl that solid granular 'catalysts consisting of or comprising chromiuml oxide, especially a dark, unglowed variety, is a highly desirable material for this purpose. Other dehydrogenation catalysts known to the art, especially bauxite impregnated with a minor amount of an-alkali metal oxide such as barium oxide and the like, may be used. The dehydrogenation pressure should not be very high, that is generally it should not exceed 50 or 100 pounds per square inch gauge, and in most instances it should be only slightly above atmospheric. At times a. subatmospheric pressure may beused, but although a low pressure favors the dehydrogenation reaction, subatmospheric pressures will generally not be used in plant operations. A low partial pressure ofthe hydrocarbon material present along with a total pressure above atmospheric may be realized by-dehydogenating the hydrocarbons in admixture with a gas such as nitrogen, steam or the like as is known to the art. Although thepresence of free hydrogen tends to have an adverse mass action cect, a small amount of free hydrogen in the charge stock often appears to have a beneficial eect upon the catalyst, especially on the intial portions of the catalyst with whichthe charge stock comes into contact. Other modiiications of dehydrogenation operation known to the art may also be used.

With a given dehydrogenation pressure and cata-I lyst activity, the dehydrogenation temperature and reaction time will be interdependent and will havein general an inverse relationship. vThe dehydrogenation temperature will be -within the range known for catalytic dehydrogenation, butA with gradually increasing temperatures as a particular body of catalyst becomes deactivated. With a fresh body of active catalyst, which will produce satisfactory dehydrogenation at a relatively low temperature, a iiow rate adapted to give dehydrogenaton not far short of equilibrium, may be used. If this flow rate is maintained as the temperature is increased, to provide for a relatively constant extent of conversion as the catalyst becomes less active, the reaction conditions will generally be such at the higher temperatures that excessive deleterious secondary or side reactions are not encountered. The catalytic dehydrogenation may be carried out in a single step as shown or may be carried out in two or more steps with separation of hydrogen between steps and ldesired also a concentration of olens produced by a previous dehydrogenation step. Such operation to be considered included in the broad as; cts of dehydrogenation unit i2 with suitable auxiliary sepa: ting equipment, being included as will obvious to skilled in the art. preliminary dehy drogenation may be conducted before the ma teri i is charged to process in which case a hydrocarbon fraction separated from the eiiuent thereof can be charged through pipe it.

When more than one dehydrogenation step is used it will generally be -found desirable to pass the recycle material from separating unit 52 through pipe G3 to the inlet of the second dehydrogenation unit as would be the effect if the material charged through pipe i Were separated from a, preliminary dehydrogenation unit..

The conversion eiected in the low pressure pyrolysis zone 'I6 is such as to produce from the unsaturated Cz--Ca hydrocarbons charged through pipe 14 an optimum yield of ylow boiling dioleflns of the nature of butadiene, pentadiene, cyclopentadiene and the like. As disclosed in the copending application of Frey,v Serial No. 396,344, filed June 2, 1941, it has been found that such optimum conditions exist when the reaction is carried out in a temperature range suitable for the production of low boiling aromatic hydrocarbons and for a period of time such that only a minor portion of such aromatica is produced. More specifically the conversion should be at a low pressure similar to that discussed for dehydrogenation unit I 2 at a temperature within a range of about 1300 to 1'100o F. preferably between about 1375 and 1550" F. for a period of time such that the ellluent contains not more than aboutA C3 material being condensed that substantially none of the C4 material escapes in the vapor phase in the overhead product. This has been found to be a simple and inexpensive way to obtain the desired separation, but it will be appreciated by those skilled ln the art that other means for separating the efiluent of any of the conversion steps may be used. The absorbent employed in absorber 23 may be a light absorption oil which is used in the closed cycle as discussed. In some instances, it may be found desirable to use a highly volatile absorpton liquid such as butane or pentane in which case it will generally be found necessary to recover vaporized absorbent from the gaseous material passing through pipe 2Q.

.It will be appreciated that the drawing is diagrammatic and that the application of my invention on a commercial scale will reduire the use of numerous pieces of conventional equipment such as pumps, heaters, coolers, separators, accumulatcrs and the like not .shown in detail but which may he readily adapted for any particular instalr lation by one skilled in the art. No pumps or compressors for the various streams have been. shown but the general i'low of each stream has been indicated and discussed as has been the preferred operating conditions for each part ci' the process and suitable equipment can be readily supplied as may be found necessary in any particular case. The general process operating conditions and material flows have been disclosed and discussed sufficiently to serve as eiicient guides for such purposes. It will be obvious to those skilled in the art that various modifications of my invention may be practiced as being included in the spirit of the disclosure and in the scope of the claims.

As an example of my process, normal butenes separated from the efiluent of a dehydrogenation of normal butane, are introduced to the process through pipe I0 and are passed in admixture with recycle butenes from pipe 63, and in admixture with an inert diluent to dehydrogenation in unit I2, which is conducted in the presence of a catalyst comprising bauxite impregnated with ve per cent barium hydroxide.' The inert diluent material comprises nitrogen and the amount of such material is adjusted so as to provide a partial pressure of butenes within the dehydrogenation unit of about 0.25 atmosphere` under the conditions of the reaction. The reaction is conture of about 1225 F. The mixture of butenes Gli ducted under a total pressure of about one atmosphere to provide a positive pressure through the apparatus, and a dehydrogenation temperaand nitrogen-ispassed through the dehydrogenatlon unit at an effective space velocity of about 995 volumes per volume of catalyst per hour. The' eilluent from the catalytic dehydrogenation unit I2 has a composition on a diluent-free basis,

\ shown in column A5 of the table and is vpassed to enlarged reaction chamber which should be quite Y.

large in cross section in comparson to the cross section of the tube coil in which the preheating is carried out. The absorption units I5 and 80 may be operated under more or less similar conditons and in order to obtain efficient separation without excessive amounts of refrigeration should be operated at substantial superatmcspheric pressures as discussed. The absorption liquid is provided by condensation of the heavier portion of the material charged to any one of the absorbers with a. sumcient amount of the Cz and separating means I5, which separates the eilluent from unit I2 into a light fraction having a composition, on a diluent-free basis, as shown by column 6, anda high-boiling fraction as shown in column 8, with the aid lof an absorption oil.

This light fraction together with the low-boiling eilluent from absorber-fractionator 80, to be diS- cussed, is passed to absorber 23 for separation of hydrogen, methane, and nitrogen from hydrocarbons heavier than methane. Such heavier hydrocarbons comprising essentially Cz and C: hydrocarbons are separated from absorbent used in absorber 23 and are passed to conversion coill vgenation to a first separation means, separating 18 through pipes 3| and 34.

said enluent into a C2 and lighter fraction essen- Y.

[Per cent by weight] 4y 's e A'1VA s Etiluent Component Charge to Emuent Low-boiling High-boiling from cata- Low-boiling Material in High-boiling thermal from thermal fraction from fraction from lytic defraction from pipe 3l from fraction from unit 76 V unit 76 absorber 80 absorber 80 hydrogenaabsorber 15 stripper 30 absorber 15 tion unit l2 14. l 25. 4 l. 80 0. 54 3. 38 94 54. 5 63. l 43. 7 14. 05 6. 30 23. 8 l. l5 5. l5 1. 34 9. 91 8. 30 0. 65 0. 20 l. 22 2.03

o. s3 1. 87 49.1 0. 36 0. 8l 0.28

Total 100. 00 100. 00 100. 00 100. 00 100. 00 100. 00 100. 00 100. 00

The heavier fraction of the eilluent from the catalytic dehydrogenation unit I2 is removed from the bottom of absorber-fractionator i5 and is passed to the separating unit 62.

An unsaturated Cz-Cs mixture of hydrocarbons is passed to the thermal conversion coil 16 in furnace 11, and is introduced to the coil through pipes 34 and 14. This charge stock, has a composition as shown in column 1 of the table, and is composed of C2 and Ca hydrocarbons produced in unit i2 plus recycled Ca and Cs hydrocarbons from the eiiluent of coil 16. This charge is reacted at about atmospheric pressure and an average temperature of about 1470 F. for a reaction time of one second; The eiiluent from coil 16 has a composition as shown in column 2 and is passed to the absorber-fractionator 80. From absorber-fractionator 80 a' low-boiling material is separated through conduit 82 with a composition as shown in column 3. and `is passed to absorber 23, as mentioned.

A higher boilingV hydrocarbon material having a composition as shown in column 4A is passed from a low point of absorber 80 through pipe 9@ to separating unit `iii. From separating unit 62,

- butadiene is removed through conduit 65 and butenes are removed through conduit S3. The butenes so removed are passed to the catalytic dehydrogenation unit i2, as previously mentioned.

From the material charged to separating unit 62 through both conduits 60 and 93 is separated a butadiene concentrate and a C2-C3 fraction. Approximately 13.6 per cent butadiene is obtained from the lmaterial charged through these two conduits. The Cz-Ca fraction is passed -drocarbons of 4 to 5 carbon latoms per molecule,

which comprises subjecting a hydrocarbon material comprising such hydrocarbons predominantly of a single carbon skeleton structure and a single number of carbon atoms per molecule to dehydrogenation `conditions of ltemperature and pressure to form a correspondingdiolefln together with minor amounts of lower-boiling unsaturated hl'- drocarbons, passing an eilluent 4of said dehydrotially free of C4 hydrocarbons and into a C2 and heavier fraction essentially free of methane, passingsaid Cz and lighter fraction to an absorption means, passing a lean absorption oil to said absorption means, maintaining in said absorption means absorption conditions such as to remove substantially vall Cz and heavier hydrocarbons from methane and lighter gases, removing absorbed material from the resulting rich absorption oil and passing at least a portion thereof to a thermal conversion step, passing said Cz and heavier fraction from said first separation means to a second separation means, separating from said second separating means a C21-Cs hydrocarbon fraction and passing same to said thermal conversion step, treating said hydrocarbons passed to said thermal conversion step at an elevated conversion temperature and a low pressure to produce an optimum yield of low boiling di' oleflns, passing the eiliuent of said conversion to a third separation means, separating said eluent l into a C2 and lighter fraction essentially free of C4 hydrocarbons and a C2 and heavier fraction essentially free of methane, passing said Ca and lighter fraction to the aforesaid absorption means, passing said C2 and heavier fraction to s'aid second separating means, and recovering from said second separating means low boiling diolens produced by said dehydrogenation and by said conversion.

2. The process for the production of butadiene from C4 hydrocarbons more saturated than butadiene 'comprising normal butane and normal butenes which comprises dehydrogenating said more saturated C4 hydrocarbons to butadiene with the simultaneous formation oi. unsaturated' C2 and C3 hydrocarbons; separating the eiiiuent of said dehydrogenation into a lighter fraction comprising C2 and Ca hydrocarbons together with lighter gases and a heavier fraction comprising Ca, C: and C4 hydrocarbons; separating C2 and C3 hydrocarbons from the lighter gases in said lighter fraction and subjecting said hydrocarbons to treatment at an elevated temperature at low pressure eilectingconversion of at least a part of said C2 to Ca hydrocarbons to butadiene with the simultaneous formation of C4 hydrocarbons more saturated than butadiene; separating the eiliuent of said high temperature conversion into 'a lighter fraction comprising C2 and C3 vhydrocarbons together with lighter gases and a heavier fraction comprising Cz, Cs and C4 hydrocarbons; admixing the last said lighter fraction with the ilrst said lighter fraction prior to the subsequent separation of lighter gases; admixing the heavier fraction from the dehydrogenation eiliuent with the heavier fraction from the eiuent of said high temperature conversiong. separating butadiene from the resulting mixture as product; separating C2 and C3 hydrocarbons from said mixture and passing said hydrocarbons to said high temperature conversion; and separating C'hydrocarbons 'more saturated than butadiene from said mixture and passing said hydrocarbons to said dehydrogenation step.

8. The process for the production of pentadiene from C hydrocarbons more saturated than pentadiene comprising normal pentane and normal pentenes which comprises dehydrogenating said more saturated C5 hydrocarbons to pentadiene with the .simultaneous formation of unsaturated Cz and Ca hydrocarbons; separating the eiuent of said dehydrogenation into a lighter fraction comprising Cz and Cz hydrocarbons together with lighter gas and a heavier fraction comprising C2 to C5 hydrocarbons; separating and hydrocarbons from the lighter gases in said lighter fraction and subjecting sa-icl hydrocarbons to treatment at en elevated temperature at low pressure eiecting conversion oi at least a part of said C2 to C3 hydrocarbons to pentadiene with the simultaneous formation of Cs hydrocarbons more saturated than pentadiene;l separating the effluent o said high temperature conversion into a lighter fraction comprising C2 and C3 hydrocarbons together with lighter gases and a heavier fraction comprising Cz to C5 hydrocarbons; admixing the last said lighter fraction with the first said lighter fraction prior to the subsequent separation of lighter gases; admixing the heavier fraction from the dehydrogenation eiiluent with the heavier fraction from the emuent cf said high temperature conversion; separating pentadiene from the resulting mixture as product; separating Ca and C3 hydrocarbons from said mixture and passing said hydrocarbons to said high temperature conversion; and separating C5 hydrocarbons more saturated than pentadiene from said mixture vand passing said hydrocarbons to said dehydrogenation step.

4. The process for the production of isoprene from iso-C5 hydrocarbons more saturated than isoprene comprising isopentane and isopentenes which comprises dehydrogenating said more saturated iso-C5 hydrocarbons to isoprene with the simultaneous formation of lmsaturated C:

yand C3 hydrocarbons; separating the eiliuent of said dehydrogenation into a, lighter fraction i comprising C2 and C: hydrocarbons together with lighter gases and a heavier fraction comprising Cz to C5 hydrocarbons; separating C: and C3 hydrocarbons from the lighter gases in said lighter fraction and subjecting said hydrocarbons to treatment at .an elevated temperature at low pressure effecting conversion of at least a part of said C2 to C: hydrocarbons to isoprene with the simultaneous formation of iso-C5 hydrocarbons more saturated than isoprene; separating the efiiuent of said high temperature conversioniseparating isoprene from the resulting mixture as product; separating Cu and Ca hydrocarbons from said mixture and passing said hydrocarbons to said high temperature conversion; and separating iso-C5 hydrocarbons more saturated than isoprene from said mixture vand passing said hydrocarbons to said dehydrogenation step.

5. A process for the conversion of normal butane to butadiene, which comprises subjecting normal butane to a catalytic dehydrogenation to form butadiene, smaller amounts of C2 and C3 unsaturated hydrocarbons being simultaneously formed by side reactions, passing eiuents of said dehydrogenation to a first separating means and separating said eiuent therein into a lighter fraction comprising C2 and C3 hydrocarbons and essentially free of C4 and heavier hydrocarbons, and into a heavier fraction comprising essentially C2 to C4 hydrocarbons and free of methane and lighter constituents, passing said lighter fraction to an absorption me ns and absorbing C2 and C3 hydrocarbons irc-m the buik of the methane and lighter constit1 nts, recovering a Cz-#Cs hydrocarbon traction so absorbed, comprising aso a minor amo-init of methane and lighter constituents, and returning a portion thereof to said rst separating means, passing a further portion of said 4Cz---Cs hydrocarbon fraction to a high-temperature conversion step as hereinafter recited, passing said heavier fraction to a second separating means, recovering from said second separating means a Cz-Ca hydrocarbon fraction essentially free of methane and lighter and of C4 and heavier constituents, `admiring the last said Cz-Cs fraction with the aforesaid Cz-Ca portion and subjecting the resulting mixture to a high-temperature conversion at a low pressure under conversion conditions such as to form an optimum yield of butadiene, small amounts of more saturated normal C4 hydrocarbons being simultaneously formed by side reactions, passing eiliuents of said high-temperature conversion to a. third separating means and therein separating said emuent into a lighter fraction comprising C2 and C: hydrocarbons and free of C'. and heavier hydrocarbons and into a heavier fraction comprlsing essentially Cz to C4 hydrocarbons and free of methane and lighter constituents, passing the last said lighter fraction to the aforesaid absorption means, passing the last said heavier fraction to the aforesaid second separating means, recovering from said second separating means a normal C4 fraction comprising unreacted normal butane from said dehydrogenal tion and normal butane produced as a. by-prodversion into a lighter fraction comprising Cz' and C3 hydrocarbons together with lighter gases and a heavier fraction comprising C: to Cs hydrocarbons; admixing the last said lighter fraction with the first saidlighter fraction prior to the subsequent separation of lighter gases: admixing the heavier fraction from the dehydrogenation eiiluent with the heavier fraction from the eilluent of said high temperature conuct of said high-temperature conversion and passing same to' said dehydrogenation, and recovering also from said second separating means as a product of the process a. butadiene fraction comprising butadiene produced by dehydrogenation of normal butane and butadiene produced by conversion of Cz--Cs hydrocarbons.

6. I'he process of claim 1 in which a portion ofthe absorbed material removed from said rich absorption oil is passed to saidnrst separation means. l

7. The process of claim 1l in which a portion of the absorbed material removed from said rich absorption oil is passed to said tlrst separation means, and recovering also from said second separating means a hydrocarbonv material corresponding to said material charged to said dehydrogenation and containing vhydrocarbons lighter gases, passing atleast a portion of enluent from said dehydrogcnation and from said thermal conversion step, and passing same to said dehydrogenation. f.

8. A process for the production of low-boiling dioleiin hydrocarbons from more saturated hydrocarbons of 4 to 5 carbon atoms per molecule,

Ca-Ca hydrocarbon fraction to a. thermal conversion step, passing said C: and heavier fractionfrom said ilrst separation means to a third which comprises subjecting a hydrocarbon material comprising such hydrocarbons predominantly of a single carbon skeleton structure and a single number of-carbon atoms per molecule to dehydrogenation conditions of temperature and pressure to form a corresponding diolefln together with minor amounts of lower-boiling unsaturated hydrocarbons, passing an emuent of said dehydrogenation to `a iirst separation -means, separating saidv emuent into a C: and lighter fraction essentially `freeoi C4 hydrocarbons' and into a C:v and heavier fraction essentially free of methane, passingrvsaid C: and lighter fraction to a second separation means and separating same into a Cn-Ca hydrocarbon fraction and into. a fraction containing methane :Suid d hydrocarbons and a C: and heavier fraction essentially free of methane, passing said Cz and- 'lighter fraction to the aforesaid second separav tion means, passing said C: and heavier traction to said third separation means, and recovering from said third separation means low-boiling diolenns produced by said dehydrogenation andl by said conversion. v

' y i JEAN P. JONES. 

